Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/36—Coatings with pigments
  • D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent
  • D21H19/56—Macromolecular organic compounds or oligomers thereof obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H19/60—Polyalkenylalcohols; Polyalkenylethers; Polyalkenylesters

Definitions

• This invention relates to a process for coating paper. More particularly this invention provides coated papers which exhibit excellent water resistance, very good gloss and improved printability.
• the invention provides a process for coating paper which comprises applying tosaid paper an aqueous dispersion comprising a filler and a vinyl binder polymer prepared by a process which comprises co polymerizing vinyl esters of alpha-branched, saturated, aliphatic monocarboxylic acids with another copolymerizable ethylenically unsaturated compound, such as vinyl acetate. 7
• Processes for coating paper are well-known in the technique of paper manufacture wherein a filler and a binder are applied to the paper in an aqueous dispersion.
• the binder is generally casein or starch although styrenebutadiene copolymers, butadiene-methyl methacrylate copolymers or acrylate-vinyl acetate copolymers are sometimes additionally employed.
• the filler-used is tities and possess the property of being rapidly dispersible.
• the binder is a vinyl polymer of an alpha-branched, saturated, aliphatic monocarboxylic acid and certain ethylenically unsaturated compounds
• the papers exhibit improved properties such as excellent water resistance, improved gloss and improved printability. Improved results and properties are also achieved when these vinyl polymers are used in combination with the conventional binders such as starch and casein.
• Paper coating is an important part of the paper industry. It is a wide field which includes the application of many different types of coatings to the base paper.
• the present process may be utilized in any process in which paper is pigment coated wherein an aqueous mixture of pigment and adhesive (binder) is applied to the surface of paper. Therefore, the essential novelty of the present process is the use of a particular adhesive or binder in otherwise well-known paper coating processes.
• pigment coating there are three basic raw materials used in pigment coating: (1) the pigment, (2) the adhesive used for bonding the pigment, and (3) the base paper, or raw stock, to which the pigment is bonded.
• the coating mixture is usually prepared by dispersing the pigment and adhesive separately in water and then mixing the two together. After the coating mixture has been prepared, it must be applied to the paper in the coating process, which generally consists of applying the fluid coating mixture to the base paper, smoothing, drying and calendering the coating. While all these steps are important in order to obtain a satisfactory coating, their control forms no part of the instant process.
• the present process may employ off-machine or machine coating techniques.
• Off-machine coating is carried out as a separate operation in a coating plant, whereas machine coating is carried out on the paper machine as an integral part of the papermaking operation.
• machine coating techniques are growing in popularity, there are still circumstances under which it is more feasible to coat by the off-machine method.
• the paper is coated and dried at'normal paper machine speeds using either the wet-end coating or size press coating techniques.
• the most important processes include brush coaters (exclusively for off-machine coating); smoothing roll coaters; roll coaters, including the planographic roll coater and the rotogravure roll coater; knife coaters, including the Champion knife coater,.trailing blade coater, the Champfiex coater, and the Kohler coater; and airknife coaters.
• a very suitable coater for use in the present process is the air-knife coater wherein an excess of coating is applied to the paper by roll applicator and the excess coating is thus blown off the sheet by means of a thin air jet which strikes the wet coating at an angle where the sheet is wrapped around a breast roll.
• any pigment which has the physical and chemical properties which are necessaryfor paper coating may be employed in the present process.
• a good pigment should possess all or most of the following properties: good dispersibility in water, correct particles size distribution, high opacifying power, high brightness, low
• pigments include, among others, titanium dioxide, precipitated calcium carbonate, water-ground calcium carbonate, calcium sulfate, calcium sulfite, barium sulfate, satin white, zinc pigment, diatomaceous silica, and color pigments such as chrome yellows, Umbers, cobalt green, Malachite green, sienna, red lead, lampblack, etc.
• the binder (herinafter sometimes called latex) which is utilized in the present process is a polymer preferably prepared by copolymerizing vinyl esters of alphabranched, saturated, aliphatic monocarboxylicacids with another copolymerizable ethylenically unsaturated compound, preferably vinyl acetate.
• this copolymer latex may contain a small amount of an a,,B-ethylenically unsaturated carboxylic acid such as methacrylic acid, acrylic acid, crotonic acid, itaconic acid, and the like, and is preferably acrylic acid. In general, less than acrylic acid is employed, and preferably from 1 to 3% is employed.
• the presence in the copolymer latex of l to 3% acrylic acid results in an increased freezing-thawing stability of the latex, so that the latex can be kept for a longer period of time under extreme conditions.
• the saturated, aliphatic monocarboxylic acids whose carboxyl group is attached to a tertiary or quaternary carbon atom will usually, in this specification, be referred to as branched or alpha-branched monocarboxylic acids.
• those monocarboxylic acids may well be used which are obtained by reacting formic acid or carbon monoxide and water, with olefins, or with paraffins in the presence of hydrogen acceptors such as olefins or compounds, such as alcohols and alkyl halides, from which olefins can be obtained by splitting off water or hydrogen halide, respectively, under the influence of liquid acid catalysts such as sulfuric acid, phosphoric acid or complex compositions of phosphoric acid, boron trifluoride and water.
• hydrogen acceptors such as olefins or compounds, such as alcohols and alkyl halides
• mixtures may contain both branched and unbranched acyclic olefins as Well as cycloaliphatic olefins.
• a mixture of saturated acyclic and cycloaliphatic monocarboxylic acids is obtained therefrom.
• preferred alpha-branched saturated aliphatic monocarboxylic acids may be represented by the general formula wherein R and R are alike or unlike and are each an alkyl group; R is a hydrogen atom or an alkyl group, said monocarboxylic acids contain at least 9 carbon atoms in the molecule.
• the vinyl esters of the said monocarboxylic acids branched at the alpha position may be prepared from the acids by known techniques, for instance, by reaction of the acid mixture with vinyl acetate in the presence of a mercury salt, or by reaction of the acids with acetylene in the presence of zinc, cadmium or mercury compounds.
• the vinyl esters of monocarboxylic acids bran'ched at the alpha position are preferably copolymerized with other copolymerizable ethylenically unsaturated compounds, containing on either side of the double bond or bonds up to about 8 carbon atoms.
• Examples of such compounds are vinyl acetate; vinyl esters of other carboxylic acids, such as pivalic acid; vinyl chloride; vinylidene chloride; acrylonitrile; esters of unsaturated carboxylic acids, such as methyl acrylate, ethyl methacrylate, dietliyl maleate and dibutyl fumarate; and unsaturated hydrocarbons, such as ethylene, propylene, styrene; alkyl substituted styrenes; conjugated dienes such as butadiene, isoprene, and the like.
• the ratio of vinyl esters of alpha-branched acids'to the other copolymerizable ethylenically unsaturated compound may vary widely. In general, however, the copolymer will contain from about 10 to by weight of the vinyl esters of alphabranched acids and from about 20 to by weight of the other copolymerizable ethylenically unsaturated compound, i.e., vinyl acetate.
• Preferred latex polymers contain from about 20% to 65% vinyl acetate, from 35 to 80% by weight of alpha-branched, saturated, aliphatic monocarboxylic acids containing'frorn 9 to 19 carbon atoms in the acid portion, and preferably 9 to 11 carbon atoms, and, optionally, from 1 to 3% by weight of acrylic acid.
• the coplymer latex may be prepared by known techniques described in U.S. 3,186,974 by Verberg; copending U.S. :patent application Ser. No. 251,767, filed Jan. 16, 1963, by Grommers and Vegter, now U.S. 3,294,727, issued Dec. 27, 1966; copending U.S. patent application Ser. No. 350,528 filed Mar. 9, 1964, by Grommers and Vegter, now U .S. 3,370,031, issued Feb. 20, 1968; and U.S. patent application Ser. No. 393,771, filed Sept. 1, 1964, by Grommers and Vegter and now abandoned.
• the polymerization may be effected according to known techniques, both with and without diluents.
• diluents When using diluents one can distinguish between polymerization in solution and polymerization in aqueous dispersion.
• emulsifiers and/or protective colloids are as a rule used, stirring being applied as desired.
• the copolymerization is initiated and/or catalyzed by conventional means.
• substances supplyingfree radicals are added, such as peroxides, for instance benzoyl peroxide and ditertiary butyl peroxides and other peroxy compounds, such as potassium persulphate and hydrogen peroxide, and diazo compounds, such as alpha-alphaazoisobutyronitrile. Often also redox systems are used.
• the temperatures usually vary between 30 and 150 C., particularly between 50 and 90 C. Polymerization may also be promoted by irradiation, particulary with ultraviolet light. I
• the latex binder may be advantageously employed in combination with casein and/or starch.
• the latex/ casein weight ratio in the total binder may vary within wide limits. Preferable latex/casein weight ratios are between 20:80 and 90:10. A very suitable ratio was found to be between 50:50 and 75:25.
• the latex/starch ratios are the same as latex/ casein. V i
• the pigment to binder weight ratio will vary widely depending, of course, upon many factors, especially the coating means employed; however, the pigmentzbinder weight ratio will usually be :between :30 and 100:10.
• Softening agents or plasticizers include invert sugar, sorbitol, urea, glycerine and corn syrups as well as resin latices, ethanolamine soaps, alkyd resins, fatty acid esters, soaps and polyglycols.
• vThe percent solids in the final coating dispersion may vary quite widely depending upon, many factors such as coating technique, machine speeds and paper end uses. It
• any raw paper stock which is customarily used or which can be effectively coated can be employed in the present process. No discussion is believed necessary herein relevant to theraw stock which-may be employed except to note that most raw stock is made from lightly beaten, weakly sized stock which may be obtained by any conventional pulp process such as the sulfite, soda or sulfate processes.
• a typical coating raw stock is as follows: to 50% supporting fibers, 40 to 70% filler fibers, 5 to 15% filler pigment, 1 to 10% sizing and other ingredients and .40 to 60% air.
• the coat weight applied to the base paper in .the coating operation is primarily determined by the percentsolids in the coating mixture but will generally range, from about 0.0001 to 0.001 inch.
• a typical film thickness of a wet coating is from about 0.0014 to 0.0017 inch for a book paper coated with 25 pounds of coating per ream (25 x 38500) on two sides, using a coating mixture between and dry solids.
• the coating may be smoothed or leveled, dried and then calendered and/or cut to size by well-known techniques.
• Printing penezration A drop of dibutylphthalate colored with Sudan red is spotted on a disc of an I.G.T. Printability Tester (developed by Research Institute for Printing and Allied Industries, TNO, Holland). A print on a strip of the coated paper to be tested is immediately made with falling pendulum and the drop is squeezed out to an eliptically shaped blot. Smooth, well-closed paper shows a long, drawn spot; rough, porous papers, a short one. The volume of the drop was kept constant with the aid of a syringe.
• the penetration is inversely proportional to the spot length. As a measure of a degree of penetration, it is customary to quote the reciprocal of the spot length as 1000/ spot length in millimeters. This volume was determined as an average of at least 10 separate measurements.
• Dennison pick resistance The pick resistance of coated paper is its ability to resist lifting of the coating away from the surface of the papers during printing, which is usually due to the tack of certain inks.
• the pick resistance or pick strength was determined using the Dennison Standard Waxes, a series of waxes having graduated adhesiveness increasing from 2 to-20. To carry out the test, the end of the wax stick is softened over an alcohol lamp and then pressed against the paper. After 15 minutes cooling, the stick is pulled vertically from the paper. The lowest numbered wax that picks gives its value. This test, of course, is: only used as a rough indication and is generally carried out on at least 5 different places on the paper sample.
• Density of print (bookprinting .offset).For both bookprinting and offset, a print is made with a special black ink developed for use with the I.G.T. Printability Tester. For bookprinting an aluminum printing form is used and for offset, a rubber covered printing form is used. The sector of the Printability Tester to which the test strips are attached is turned by hand.
• test strips After 24 hours of dying, the test strips were compared to assess visually the degree of blackness.
• A 450 ft. /min.
• M 560 ft./min.
• B 650 ft./min.
• Striking-in This test is carried out using the I.G.T. tester by making a print of a black, light viscous ink on the test paper, by turning the pendulum by hand. Immediately after the print is made, the printed test strip on the sector is covered with a strip of good art printing paper. One-third of the sector, with both strips, is allowed to descend, in touch with the printing form, 5 seconds after the first print is made. The second third of the sector is released after 30 seconds and the last third, after 60 seconds. Slight striking-in is associated with transference of a large quantity of link to the art paper. More rapid striking-in is characteristic by transference of less ink. The rapidity of striking-in is determined on the basis of density of the ink transferred to each part of the art paper strip.
• Wet rub resistance This test is well known in paper coating industries wherein a piece of test paper of an appropriate size is brought in contact with water for 15 seconds. This is done by keeping the paper with the coated side downwards on the water surface. Subsequently, the paper is removed from the water and after 15 seconds the coated side is rubbed with the thumb. The thumb is then rubbed onto a sheet of black paper. -Any pigment loosened by the water can easily be seen on the black surface after it has dried. The intensity of the deposit of color depends on the water resistance of the coating and/ or the number of rubs. The higher the numerical rating (-10) the better the wet rub resistance.
• the vinyl esters of alpha-branched, saturated aliphatic monocarboxylic acids used in the examples were prepared from alpha-branched acids containing from 9 to 11 carbon atoms as follows:
• a fraction was taken of a product obtained by thermal cracking of a parafiinic base material in the vapor phase in the presence of steam, which fraction consisted for the greater part of alkanes with 8 to 10 carbon atoms.
• This fraction was partially hydrogenated to convert any dienes present in alkenes. After this hydrogenation the alkenes constituted 76% by weight of the mixture, of which 39% by weight were straight-chain, by weight were branched and 17% by weight were cyclic alkenes, while double bonds at terminal carbons hardly occurred.
• the balance of the mixture consisted of saturated hydrocarbons (17% wt.) and aromatics (7% wt.).
• the olefins were converted into monocarboxylic acids at 60 C. in a reaction mixture while the composition was kept constant.
• the hydrocarbon mixture containing the olefins was fed at a rate of 0.7 l./h.
• the catalyst which consisted of H 0 BF and H 0 in the molar ratio of 2:3:2, was fed at a rate of 1.4 l./h.
• the liquid part of the reaction mixture was kept at a volume of 3 liters.
• the liquid was kept under a carbon monoxide pressure of 70 atmospheres absolute. Vigorous stirring was applied.
• the apparatus consisted of chrome-nickel steel.
• the phase containing the mixed carboxylic acids was washed continuously and countercurrently at 40 C. with 5% by volume of water and subsequently at 20 C. also continuously and countercurrently successively with another 10% by volume of a 1% solution of sodium citrate in water and with 10% by volume of a 5% solution of sodium bicarbonate in water.
• the mixed monocarboxylic acids were extracted from it continuously with excess ammonia in water. From the solution of the ammonium salts the free and bound ammonia was evaporated continuously. The mixed monocarboxylic acids separated as a liquid, and were subsequently dried and distilled in vacuo.
• Dry acetylene was passed at a rate of 60 l./ h. through a vessel in which the said monocarboxylic acids were kept at 200 C.
• the mixture of acetylene and vapor of the monocarboxylic acids was passed through a quartz tube with a diameter of 25 mm., which was kept in an electric furnace at 300-330 C. This tube was 45 cm. long and was filled with 150 ml. of said catalyst.
• the vapors 8 leaving the tube were condensed.
• the condensate which contained vinyl esters and also non-converted monocarboxylic acids, was distilled in vacuo.
• the vinyl esters (70% m.) Were distilled at a pressure of 0.5 mm. Hg. at -65 C. To remove traces of mono carboxylic acids, the vinyl esters were washed with dilute caustic soda and with water.
• vinyl esters were then copolymerized with vinyl acetate in emulsion in the weight ratios of vinyl acetate: vinyl esters of alpha-branched monocarboxylic acids of :50; :40 and :35.
• copolymerizations were performed in the same manner in a flask with a stirrer, reflux condenser and thermometer.
• Vinyl acetate vinyl esters of alpha-branched saturated monocarboxylic acids contained 9-11 carbon atoms (wt. ratio):
• the pigment dispersion was made by stirring for about two hours in a slow paddle mixer a slurry of'clay in water to which a small amount of wetting agent had been added.
• the starch solution was made as a 20% wt. solution by cooking the starch, while stirring, with the required amount of water until a temperature of 90 C. had been reacted. The solution was kept at this temperature for about 10 minutes, after which it was applied by adding it to the pigment dispersion. At the end Vinyl Latex A was added and the total mixture stirred until homogeneous.
• the resulting coating compositions were applied to bleached kraft paper of about g./m. machine glazed 79 10 on one side only using the air knife coating technique de-
• the pigment dispersion was made by stirring for'about scribed hereinbefore. two hours in a slow paddle mixer a slurry of clay in
• various commercial resins were subwater to which a small amount of wetting agent had been stituted for the various vinyl latices. The proprietary added.
• the slurry was rendered alkaline to prevent the resins were as follows: occurrence of pigment shock during the subsequent addi- Name or designation 7 7 Composition tion of alkaline casein solutions.
• the papers coated with the starch/vinyl polymer latex which is often desired for printability purposes.) After binders and proprietary binders were tested using the tests addition of the cutting agents the mixture was stirred for hereinbefore described. The test results and evaluations 25 minutes before application.
• Oil N falling pendulum 2 2 3 0 3 6 4 Oil L, falling pendulum 10 10 10 4 10 10 10 10 Oil L, spring drive-device, A 7 7 9 0 8 10 10 Oil L, spring drive-device, M 5 5 9 O 6 10 10 Oil L, spring drivedevice, B. 3 3 6 0 4 6 4 I.G.T. pick (ofl'set):
• Oil N falling pendulum. 0 2 3 0 O 3 3 Oil L, falling pendulum-i. 10 10 10 4. 5 10 10 10 Oil L, spring drive device, A.-. 6 8.5 10 0 7 10 8 Oil L, spring drive device, M... V 4.5 6 9 0 3. 5 9 7 Oil L, spring drive device, B... 3 5 7. 5 4 4 7. 5 6 Wet rub resistance 7. 5 7 S. 5 4 8 8. 5 142. a 150 172. 5 s1. 5 136. 5 176. 5 169 1 In combination with starch.
• Pigment dispersion EXAMPLE III China Clay S.P.S. g 2000 5 Calgon S (10% t cc 60
• the procedures of Examples I and II were substantially Water cc 890 repeated wherein the vinyl latex was a terpolyrner of NaOH (10% wt.) cc 50 (1) vinyl acetate, (2) vinyl esters of alpha-branched, NH OH (25% wt.) cc 6 saturated, aliphatic monocarboxylic acids containing 9 Nopco NDW (defoamer) cc 4 to 11 carbon atoms in the acid portion and (3) acrylic Casein solution: acid in the weight ratio of 65:35: 1.
• a process for coating paper which comprises first NI-I OH (25% wt.) cc 12.5 applying to the surface of said paper an aqueous dispersion comprising (A) 100 parts by weight of pigment and (B) from to parts by weight of a binder comprising (1) from 20 to 90 parts by weight of a material selected from the group consisting of starch and casein and (2) from 10 to 80 parts by weight of a vinyl terpolymer latex comprising from 20 to by weight vinyl acetate, from 35 to by weight of vinyl esters of alpha-branched, saturated aliphatic monocarboxylic acids containing from 9 to 19 carbon atoms in the acid portion and from 1 to 3% by weight of acrylic acid, and then drying said coated paper.
• a process as in claim 1 wherein the pigment to binder weight ratio is between :20 and 100: 10.

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Cited By (10)

Citations (11)

• 1965
  • 1965-10-26 NL NL6513811A patent/NL6513811A/xx unknown
• 1966
  • 1966-10-06 US US584670A patent/US3477871A/en not_active Expired - Lifetime
  • 1966-10-24 GB GB47602/66A patent/GB1133237A/en not_active Expired
  • 1966-10-24 BE BE688787D patent/BE688787A/xx unknown
  • 1966-10-24 SE SE14512/66D patent/SE300081B/xx unknown
  • 1966-10-24 DE DE1696258A patent/DE1696258B2/de active Pending

Patent Citations (11)

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